This device was the first effect pedal ever created by BOSS. While chorus was starting to gain acceptance in the late 70s in rack form, Roland decided to create this footpedal-based effect under the BOSS name. The standard set by this pedal (with regard to tone) is still in use today. This pedal was popularized by Andy Summers of The Police, Jeff Baxter of the Doobie Brothers, and Alex Lifeson of Rush. This pedal is said to have a very swirly tone, which is the combination of the chorus and vibrato effects. This is not a compact pedal form, it's actually a semi-large device with two footswitches, one for each effect. A power supply was required for this effect, it could not run off a 9V battery. A noted problem with this early BOSS effect was the horrible drain on a signal it produced while bypassed. Many modifications are frequently done to it to remove this flaw. This is a very hard pedal to track down these days, often going for multiple hundreds of dollars on auction sites.